Exploring the EM-wave diffusion capabilities of axicon coding metasurfaces for stealth applications.

Coding metasurfaces for diffusion scattering of electromagnetic (EM) waves are important for stealth applications and have recently attracted researchers in physics and engineering communities. Typically, the available design approaches of coding metasurfaces lack a coding sequence design formula and sometimes cannot simultaneously ensure uniform diffusion and low reflected power intensity without extensive computational optimization. To the authors' best knowledge, the diffusion and radar-cross-section reduction (RCSR) of 2D axicon metasurfaces for cloaking and stealth applications have not been explored before. This article presents a single-layer coding metasurface design that exhibits an axicon phase mask on its aperture for efficient diffusion of EM-waves and RCSR of metallic objects. The proposed approach is robust and ensures greater than 10 dB of RCSR for normal incidence and a wide-range of off-normal incident angles. Theoretical calculations, numerical simulations, and experimental validations of the proposed axicon coding metasurface demonstrate that the 10 dB RCSR covers the frequency range of 15 to 35 GHz (fractional bandwidth is 80%) under normal incidence. Under off-normal incidence, the RCSR and the diffusive scattering behavior are preserved up to 60° regardless of the polarization of the far-field incident radar wave. Compared to other available approaches, the presented design approach is fast, robust, and can achieve more uniform diffusive scattering patterns with remarkable RCSR, which makes it very attractive for potential stealth applications.